s390x: for clang use fp-contract=on instead of fast
s390x: for clang use fp-contract=on instead of fast

Make clang slightly more cautious when contracting floating-point
operations (e.g., when applying fused multiply add) by setting
-ffp-contract=on (instead of fast).

Signed-off-by: Marius Hillenbrand <fe1e41a2593d8a0d1128edc53cee7053b8cae934@linux.ibm.com>

xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS